The present invention relates to small-diameter rigid disc memory devices, in particular the positioning of the head or heads over the desired track for reading and writing data from and onto, respectively, the rotating disc. Head positioners can be driven by stepper motors, or be controlled by a DC servo motor system, and include either a linear or rotary actuator arm.
Various drive techniques are used in stepper motor head positioners including direct drive, band actuators and ball-screw drives. Direct drive usually provides poor resolution and screw drives are expensive. A band drive requires a capstan, the diameter of which becomes very small to achieve the desired resolution over a track on a disc having small track-to-track spacing. A small diameter capstan may impose prohibitively high stresses in the band.
A disc memory head positioner constructed according to the principles of the present invention comprises an actuator arm, mounted to a support post by a flexural pivot driven by a friction drive system pre-loaded by a tension spring. The friction drive system employs a micro-stepped stepper motor. By servo-controlling the stepper motor to track center, very accurate position over the desired track is achieved. Stepper motor holding torque is then used to hold the heads rigidly in position.
The head positioner of the present invention incorporates the advantages of a rotary-actuated arm about a pivot point. The pivot point comprises a single, flat strip, flexural pivot that supports the actuator arm while providing vertical stiffness at the attachment point as well as torsional stiffness overall.
The flexural pivot support of the present invention provides lower friction and hysteresis than is possible with typical ball-bearing and shaft designs, avoids the cost of machining parts to close tolerances, and provides much longer life than prior-art designs.
The friction drive system of the present invention provides high resolution positioning as compared to rolling band or lead screw drive systems which are usually supported by ball or sleeve bearings. Friction drive resolution is not limited by band bend radius or screw interface friction which is present in the last mentioned prior-art systems. Absolute repeatability is not required in the present system because the stepper motor is servo controlled to the tracks on the disc. It should be noted that significantly fewer parts which exclude ball-bearings are necessary to construct the positioner of the present invention.